1. Field of the Invention
The present invention relates generally to spatial resolution conversion of an image signal, and more particularly, to using single-channel interpolation if a magnitude of a motion vector is greater than a threshold value, and using multi-channel interpolation otherwise, for attaining high resolution and stability in spatial resolution conversion.
2. Background of the Invention
When an encoder reduces the size of an image to improve compression rate or when an image encoded to a SD (standard definition) level is displayed with a HD (high definition) level display, the image signal is converted for spatial resolution. Since spatial resolution conversion of an image signal has great impact on visual quality of an image, much research has been carried out on spatial resolution conversion.
FIG. 1A is a block diagram schematically illustrating a spatial resolution conversion method 10 using single-channel interpolation according to the prior art. Referring to FIG. 1A, the spatial resolution conversion method 10 performs spatial resolution conversion on an image signal in units of a single frame to generate a magnified resolution-converted image signal.
The single-channel interpolation may be a cubic-based or spline-based linear interpolation, an edge directed interpolation (EDI), or a combination thereof, as known to one of ordinary skill in the art. However, the spatial resolution conversion method 10 using single-channel interpolation cannot achieve spatial resolution improvement when aliasing is present in an image.
FIG. 1B is a block diagram schematically illustrating a spatial resolution conversion method 20 using multi-channel interpolation according to the prior art. Referring to FIG. 1B, the spatial resolution conversion method 20 performs spatial resolution conversion based on a plurality of frames. Multi-channel interpolation typically requires high computational complexity with sub-pixel based motion estimation and high-resolution image reconstruction.
Moreover, in case of wrong motion estimation, the stability of spatial resolution conversion becomes a serious issue. In other words, when accuracy of a motion estimation value for an image signal with large motion is low, degradation occurs in the visual quality of the image due to improper spatial resolution conversion.